I think it just has something to do with how your wrist joint is aligned, I know when I'm rock climbing we try to use our index finger as little as possible.

If you think about pulling on a handle (aligned vertically, like a refrigerator handle, esp. at eye level), the force is naturally concentrated closer to the bottom of your hand, around your ring finger and pinky. If you cock your wrist so that the majority of the force is being applied by your index finger, you end up with your wrist bent at a funny angle and it's just pointless.

"I'm offering straight punch, kick while downed to the ribs or head, and of course- the german suplex...which is one suplex quickly followed by another." - Guerilla Fists

Ok, on second thought, what I wrote above doesn't make that much sense, because there are definitely times in rock climbing when you would use your index finger (generally when the next handhold is small and directly above your head). However, you usually use your ring and pinky finger when the handholds are to the side, and you try to plan your route so that you're pulling sideways on the handholds. So you do end up using your fourth and fifth fingers more.

I think in judo and BJJ most of the pulling is more similar to the climbing situation where you're pulling on a grip laterally, rather than something directly above your head.

Of course, this provides no explanation of WHY this is the case, so I guess this whole answer was somewhat pointless. Maybe someone with some knowledge of anatomy will chime in now.

"I'm offering straight punch, kick while downed to the ribs or head, and of course- the german suplex...which is one suplex quickly followed by another." - Guerilla Fists

"Double knife hand strike to the nerves on the inside surface of the upper arm WHILE someone is throwing a haymaker at you with that arm. I laughed. "

I did this - to a smart ass 16 yr old in my class who said it wouldn't work. I also gave him a club, to make it more interesting. I don't know how you were shown, but this kid screamed upon impact, dropped the club then dropped to the ground. Of course, those were the good old days, before you could get sued over a broken toenail * sighs *